Adjustable camshafts for the valve gear of an internal combustion engine having an outer shaft, on which a cam element is mounted and which is connected in a rotationally fixed manner to an inner shaft, which extends through the outer shaft, serve for variable control of the inlet valves and exhaust valves of the internal combustion engine. Further cam elements are mounted on the outer shaft in a rotationally fixed manner, and if the phase position of the inner shaft is adjusted relative to the phase position of the outer shaft, the phase position of the cam elements which are rotatably supported on the outer shaft, forming a slide bearing gap, also changes relative to the phase position of the cam elements which are rigidly arranged on the outer shaft. The nested shafts rotate about a common axis of rotation in the cylinder head of the internal combustion engine and can be adjusted relative to one another in their phase position by a control element. The cam elements interact with the valves of the internal combustion engine either directly or via rocker arms, and control forces, which have to be absorbed via the slide bearing gap of the rotatable support of the cam elements on the outer shaft, act on the cam elements. It has become apparent here that in the event of a deficient lubricating oil supply to the slide bearing gap between the inner surface of the cam elements and the outer surface of the outer shaft this may result in wear, which is always something to be avoided.
The post-published patent application DE 10 2012 103 594 A1 shows an adjustable camshaft for the valve gear of an internal combustion engine, having an outer shaft and an inner shaft rotatably mounted in the outer shaft. Cam elements are rotatably supported on the outer surface, forming a slide bearing gap, and are connected to the inner shaft by a bolt in a rotationally fixed manner. In order to transport lubricating oil from the installed surroundings of the camshaft into the slide bearing gap, it is proposed to introduce at least one oil-retaining bore into the cam element, so that splash oil can be fed from the installed surroundings of the camshaft through the oil-retaining bore into the slide bearing gap between the outer shaft and the cam element by the rotation of the camshaft. Here the oil-retaining bore is situated in the cam element, which has disadvantages in the machining process. In particular, the introduction of an oil channeling groove into the inner surface of the cam bore of the cam element is costly, and it has become apparent that owing to the centrifugal forces during rotation of the camshaft the lubricating oil largely remains in the oil channeling groove, so that it is desirable to improve the passage of the lubricating oil from the oil channeling groove into the slide bearing gap.